Children's Bone need Good Food and Exercise

The skeleton is an amazing living structure.  We are all aware that our bones keep us from collapsing and provide a structure to protect our insides.  However, in addition to providing support they build blood cells, red and white cells, store chemicals, transmit sounds in the middle ear, and even make a hormone called osteocalcin.  (Osteocalcin helps the metabolic processes regulating glucose, influencing moods, keeping memory in working order and even boosting male fertility.)

Bones start growing when a baby is still inside its mother’s womb, but the skeleton is only partly complete at birth. From the top of the head to the tiniest toe, adults have about 206 bones and kids have about 300 bone “parts”.  These ”parts” continue to grow and fuse until about 25 years of age.  At first, they are cartilaginous and can bend easily but grow stronger as they fuse and become calcified.

About 70% of a bone is inorganic material such as calcium and 30% organic.  The most fundamental organic element of bone is collagen.  There are different types of collagens, one that makes the white of your eye and the collagen of bone which combines with a mineral, hydroxyapatite to make bone and teeth.  We think of bones as being inert building material, but they are living tissue growing stronger with exercise.  The bone in a professional tennis player’s serving arm may be 30% thicker than the other arm.

Calcium does not work alone to build and maintain bone strength.  Other minerals like phosphorous, magnesium and other nutrients such as Vitamins D and K.  The parathyroid glands (4 small glands behind the thyroid gland) control how much calcium is in the blood.  Low calcium equals more parathyroid hormone.

The body’s ability to store calcium decreases with age. By young adulthood bones reach their peak density and then begin to lose about 1% a year.  Low calcium intake is common among adolescent girls putting them at risk for thinning of their bones as early as 30.  Pregnant women lose calcium (3-5% of their bone mass) during pregnancy and breast feeding but can recover afterwards by consuming 1000 to 1300 mg calcium within 6 months.  Three 8-ounce glasses of milk per day will provide enough calcium.

It is important for children to build strong bones both with good diets and lots of exercise.  Good diets include calcium (milk not juice). The amount of calcium needed varies by age, with the highest requirement between 9 and 18 years old.  The stronger the child’s bone the longer it will remain strong.

Good sources of calcium include milk and dairy products, fish bones (canned salmon and sardines), and dark-green, leafy vegetables.  Non-fat milk and yogurt are good sources.  For those allergic to dairy try calcium fortified juices, tofu, green vegetables, spinach, kale and broccoli, beans and fortified cereals.

Osteoporosis happens more often in women than men, but it does happen in men. Healthy diets and exercise are important for all lifelong.

Dedicated to my friend Jane.

September 2026

by Sally Robinson MD